1. Field of the Invention
The present invention relates to a method of cleaning various parts in an electrophotographic printer and more particularly to a cleaning method where residual toner on the photoconductive drum of an electrophotographic printer is removed at predetermine timings.
2. Description of the Related Art
With an electrophotographic printer, the surface of a photoconductive drum is uniformly charged by a charging section, exposed to image light to have an electrostatic latent image formed thereon. The latent image is then developed with toner into a toner image. The toner image is transferred to print paper with the aid of Coulomb force. Sometimes, the toner on the photoconductive drum may be left not transferred to the print paper and is carried to the exposing section. If the photoconductive drum is exposed to another image light with such residual toner left on the photoconductive drum, normal exposure to subsequent image light is impaired. Thus, there is provided a cleaning section which removes the toner from the photoconductive drum with the aid of Coulomb force.
The aforementioned conventional printer suffers from the following problem. Toner left on the photoconductive drum after the transfer operation includes residual normally-charged toner with which an electrostatic latent image was developed into a toner image, and reversely-charged toner of a polarity opposite to the normally-charged toner. The cleaning roller is opposite in polarity to the normally-charged toner. Thus, the normally-charged toner migrates to the cleaning roller due to Coulomb force that acts in a direction from the photoconductive drum to the cleaning section.
The cleaning roller is of the same polarity as the charges of the reversely-charged toner so that the cleaning roller repels the reversely charge toner. Thus, the surface of the photoconductive drum passes the cleaning section with the reversely-charged toner left thereon. When the reversely-charged toner reaches the charging section, the reversely-charged toner is attracted to the charging section since the charging roller is opposite in polarity to the charges of the reversely-charged toner. The reversely-charged toner accumulates on the charging roller, causing unstable charging of the surface of the photoconductive drum.